Sometimes after formatting a Harddrive and re-installing Windows, the NTFS-Permissions for other drives are kinda corrupted (need Admin-Rights for everything, “Unknown User” is there, …).

There is a simple command-line command you can execute to reset the permissions.

1. Start “cmd” as Administrator
2. Navigate to the Drive you want to reset the permissions
3. Run the following command: icacls * /T /Q /C /RESET

After a while, your permissions are all fixed!

Source: http://lallousx86.wordpress.com/2009/06/14/resetting-ntfs-files-security-and-permission-in-windows-7/

More Info about icacls.exe